Reliability-Based Design Aid for Evaluation and FRP Retrofit of Existing RC Bending Members by Considering Project-Specific Conditions

Abstract

This paper presents the formulation of a reliability-based design aid to assess the need for strengthening existing reinforced concrete (RC) flexural members and optimize the retrofit using externally bonded fiber-reinforced polymers (FRPs) if the member is deficient. The design aid consists of evaluation charts and a simplified formula calibrated using reliability theory to consider the effect of satisfactory past performance of the assessed structure in terms of load type and magnitude seen during the service life and the redundancy of the considered structural system. The design aid was calibrated based on the design procedure given in the American Concrete Institute ACI PRC-440.2-23, “Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures,” and the Canadian Standards Association CSA S806-12, “Design and construction of building structures with fibre-reinforced polymers,” and presented in a user-friendly manner to be used by engineers experienced in the assessment and retrofit of structures. The input of the design aid consists of the member’s unstrengthened utilization ratio (demand-to-capacity) and the number of hinges to form a mechanism, while the output is the required flexural resistance to upgrade the member capacity. Numerical examples of using the design aid in structural evaluation projects are presented, highlighting the significant savings in the required amount of FRP to retrofit deficient members compared to the conventional structural evaluation method. Reliability analysis allows refined evaluation of existing structures to determine the need for retrofit and optimize the retrofit using fiber-reinforced polymers (FRPs). This can be accomplished when the reliability analysis accounts for the redundancy in the structural system and satisfactory past performance. The use of such methods in practice is hindered by the lack of user-friendly tools that can be readily used by design engineers in evaluation projects. In this research, a reliability-based design aid is developed to assess the safety of existing flexural members and optimize the retrofit using FRP by utilizing field-specific information including the redundancy of the structural system and the load history. The design aid can be used by engineers with limited exposure to reliability analysis; thus, the charts are user-friendly.